Echo canceling system

ABSTRACT

An optimal echo canceling processing is provided regardless of a condition of a partner&#39;s system and even in the condition with large delay amount and large fluctuation amplitude of a network transmission. A speaker  10  inputs a voice via a microphone  11.  A voice signal of this voice is transmitted to a terminal  14  of a conversation partner via a VoIP application  13  and the internet  30.  Concurrently, the voice signal is inputted to an echo canceller  100.  The echo canceller  100  detects sound characteristics of an echo path in advance or dynamically, adjusts a filter coefficient for generating an echo canceling signal, and receives an adjustment by a user. The echo canceller  100  generates the echo canceling signal by processing the received voice signal based on the sound characteristics and the adjusting amount. The echo canceling signal is subtracted from a response signal containing an echo that has been re-inputted from a loudspeaker  22  of the partner via a microphone  21.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an echo canceling system in afull-duplex communication system.

2. Description of Related Art

Accompanying a widespread use of the internet, various types of servicesutilizing the internet have started. For example, what is called acomputer telephony system using a technology such as VoIP via theinternet has become common. The following is a description of aconventional full-duplex communication system using the VoIP applicationvia the internet.

FIG. 13 is a diagram schematically showing the full-duplex communicationsystem. In FIG. 13, numerals 10 and 20 both denote speakers.Hereinafter, “speaker” means a person who holds a conversation by usingthe computer telephony, and “loudspeaker” means a device of the computertelephony outputting the transmitted voice. For convenience, thefollowing description is directed to an example of the case where thespeaker 10 speaks and the voice of this person is transmitted to thespeaker 20 side. Numerals 11 and 21 denote microphones, numerals 12 and22 denote loudspeakers, numerals 13 and 23 denote VoIP applications,numerals 14 and 24 denote terminals, and numeral 30 denotes theinternet. A communication interface and other devices are omitted inthis figure for convenience.

When the speaker 10 inputs voice to the microphone 11, the VoIPapplication 13 receives a voice signal corresponding to this voice andperforms necessary processings such as a sampling, so as to betransmitted from the terminal 14 to the internet 30 as packet data. Allpacket data follow respective routes on the internet and reach theterminal 24. These packet data are assembled sequentially and subjectedto necessary processings by the VoIP application 23, then outputted fromthe loudspeaker 22 as voice.

During such processings, it has been known conventionally that aphenomenon called an echo occurs. The voice outputted from theloudspeaker 22 not only reaches the conversation partner 20, butsometimes is re-inputted undesirably to the microphone 21 as voice. Inthis case, the voice re-inputted from the microphone 21 is transmittedvia the VoIP application 23 in the terminal 24, the internet 30 and theVoIP application 13 in the terminal 14, thus being outputted from theloudspeaker 12 as voice. This forms a kind of loop. In a path that formsthis loop generating the echo (hereinafter, referred to as “an echopath”), transmission delay is generated. In other words, the speaker 10hears the voice that he/she inputted to the microphone 11 from theloudspeaker 12 a little later. When this echo occurs, it is known thatthe speaker finds it very difficult to talk and listen to the voice ofthe partner. Also, when the echo level is very high so that the echodiverges without fading, a phenomenon called howling occurs. In thiscase, it is very difficult to have a conversation.

In response to this, an echo canceller has been used conventionally.FIG. 14 is a diagram schematically showing an echo canceling systemusing the conventional echo canceller. In FIG. 14, a terminal 24 on aconversation partner 20 side has an echo canceller 25. The echocanceller 25 receives a signal to be outputted via a loudspeaker 22 asan input and subtracts the received signal from a signal captured by amicrophone 21, thereby canceling a voice signal that has beenundesirably headed and re-inputted in the microphone 21.

As illustrated in FIG. 14, the conventional echo canceller has had aconfiguration that the voice signal undesirably head from theloudspeaker toward the adjacent microphone is canceled on the spot, thuspreventing this undesirably received voice signal from returning to asystem on the speaker side.

However, the echo canceling system using the conventional echo cancellerhas the following problems.

First, an echo canceller is not always installed and operated in asystem on the conversation partner side. In the conventional echocanceling, it is necessary to cancel out the undesirable path of thevoice between the loudspeaker and the microphone in the system on thepartner side (hereinafter, referred to as “a far-end undesirable path”).For this purpose, the echo canceller has to be installed and operated inthe system on the partner side. However, this is not always expected. Ifit is not installed and operated, the speaker has to ask the partner toinstall and operate the echo canceller.

Second, when performing an echo canceling processing, it is necessary toconsider not only canceling out the echo caused by the far-endundesirable path but also canceling out an echo caused by theundesirable path of the voice between the loudspeaker and the microphonein the system on the speaker side (hereinafter, referred to as “anear-end undesirable path”). The voice of the conversation partner andthe voice in the case where the far-end undesirable path is notcompletely canceled out are outputted from the loudspeaker on thespeaker side. The near-end undesirable path caused by the input of thosevoices from the loudspeaker to the microphone also has to be prevented.

Third, the speaker, who will actually hear the echo, cannot make fineadjustments to the echo canceling processing for him/herself. In aconversation, the echo causes a problem that the speaker finds itdifficult to talk and listen because of his/her own echo voice outputtedfrom the loudspeaker. Accordingly, how the speaker feels the echo issubjective. Therefore, it is preferable that, in the echo cancelingprocessing, the speaker can adjust a hearing condition of the echo forhim/herself. However, in the conventional echo canceling system, sincethe echo canceller is located in the system on the partner side, thespeaker cannot adjust the echo canceller according to the hearingcondition of the echo. Although it is possible technologically tooperate parameters of the echo canceller in the system on the partnerside by remote control, the partner side cannot accept such environmentfrom the viewpoint of security.

Such a problem also means that a user who has introduced the echocanceller in his/her own system cannot perceive the effect of itdirectly. In other words, the user who has introduced the echo cancellercan neither feel benefit of an echo canceling effect by theintroduction, nor adjust the echo canceller in order to achieve betterecho canceling effect. The echo canceller is introduced not forhim/herself but for partner side. Thus, even when a user introduces it,its cost and the benefit for the user are not balanced. This is one ofthe obstacles of the diffusion of the echo canceller.

Fourth, when voice signals are exchanged by packet telecommunication viathe internet, the condition of the echo that is heard actually by thespeaker varies easily. The echo is influenced by a transmissioncondition of a network. In a transmission of the voice signals by packettelecommunication via the internet, the delay amount of a networktransmission is large. Also, the condition of the network transmissionvaries easily because of the routing and the variation of trafficamount, leading to a large characteristic fluctuation when transmittingthe voice signals. Therefore, the characteristic amount cannot bedetermined simply from the distance between the speakers and willfluctuate even if it is calculated once. Consequently, the mereinstallation of the conventional echo canceller on the speaker side doesnot make it possible to obtain an appropriate signal for canceling theecho in a reliable manner.

SUMMARY OF THE INVENTION

In view of the problems described above, it is an object of the presentinvention to provide an echo canceling system in which a speaker canalways use an echo canceling processing regardless of a condition of aconversation partner's system, that is, whether or not an echo cancelleris installed and operated in the conversation partner's system.

Also, it is an object of the present invention to provide an echocanceling system in which the speaker, who will hear an echo, can makefine adjustments to the echo canceling processing for him/herself. Thisalso leads to the effect of the echo canceller enjoyed directly by auser who has introduced the echo canceller.

It is a further object of the present invention to provide an echocanceling system that can execute an optimal echo canceling processingeven in the condition with large delay amount and large fluctuationamplitude of a network transmission, such as in exchanging voice signalsby packet telecommunication via the internet.

In order to achieve the above-mentioned objects, an echo cancelingsystem for a full-duplex communication system of the present inventionincludes a sound characteristics detecting portion for detecting soundcharacteristics information of an echo path seen from a speaker side,and an echo canceling processing portion for canceling an echo bygenerating an echo canceling signal from a voice signal based on thesound characteristics information detected by the sound characteristicsdetecting portion and by superimposing the echo canceling signal on thevoice signal returned from a system on a conversation partner side.Those portions are installed in a communication system not on theconversation partner side but on the speaker side.

With the above configuration, the echo canceling processing can becarried out in the system on the speaker side based on the soundcharacteristics information of the echo path seen from the speaker side,so the echo canceling processing can be used regardless of aconfiguration of the system on the conversation partner side. Inaddition, it is possible to execute an optimal echo canceling processingtaking a transmission delay into account even in the condition with alarge delay amount and a large fluctuation amplitude of a networktransmission, such as in sending voice signals by packettelecommunication via the internet.

It is preferable that the echo canceling system of the present inventionfurther includes an adjusting portion for receiving a tuning signal ofan echo canceling processing by a speaker. The echo canceling processingportion generates the echo canceling signal from the voice signal usingthe tuning signal in addition to the sound characteristics informationdetected by the sound characteristics detecting portion.

With the above configuration, it is possible to carry out the echocanceling processing in the system on the speaker side based on theadjusting amount of the echo canceling processing inputted by thespeaker in addition to the sound characteristics information of the echopath seen from the speaker side.

Next, in the above configuration, when the sound characteristicsdetecting portion detects the sound characteristics of the echo path, itis preferable that the sound characteristics detecting portion includesa signal generating portion for generating a sound characteristicsdetecting signal, which serves as a reference signal, and beforestarting a conversation, the sound characteristics detecting portiondetects the sound characteristics information of the echo path seen fromthe speaker side using the sound characteristics detecting signal and aresponse signal returned from the conversation partner side. Forexample, when using white noise, an impulse signal or the like is usedas the reference signal, it is possible to detect the soundcharacteristics information of the echo path in an accurate manner. Avoice signal inputted during the conversation also may be used as thereference signal.

Also, it is preferable that, in detecting the sound characteristicsinformation of the echo path by the sound characteristics detectingportion, a threshold and a correlation search range with respect to acorrelation value between the reference signal in the system on thespeaker side and the response signal returned from the conversationpartner side can be adjusted.

This is because, in the condition with large delay amount and largefluctuation amplitude of a network transmission, it is necessary todynamically adjust the range in which the delay amount is searched, andto flexibly adjust the search range in order to suitably detect thedelay amount that varies even after it is calculated once.

Next, it is preferable that the echo canceling signal used in the echocanceling processing of the echo canceling processing portion is dividedinto a delayed part and a signal part following the delayed part, andthe echo canceling processing portion includes a delay filter forproviding a delay corresponding to the delayed part and a signal filterfor generating a signal corresponding to the signal part.

With the above configuration, the delayed part of the echo path in thesignal used in the echo canceling processing can be processed by thedelay filter, thereby reducing an arithmetic processing amount.

Next, it is preferable that the system on the speaker side includes aloudspeaker and a plurality of microphones and performs a synchronousaddition of input voice signals of the plurality of the microphones withrespect to a direction of the speaker so as to enhance a voice signal.Also, it is preferable that the system on the speaker side includes aloudspeaker and a plurality of microphones and performs a synchronoussubtraction of input voice signals of the plurality of the microphoneswith respect to a direction of the loudspeaker so as to cancel out anecho signal outputted from the loudspeaker.

By combining the input voice signal processings of the plurality of themicrophones as in the above configuration, it is possible to performprocessing of enhancing the voice signal of the speaker and that ofcanceling the near-end echo signal.

The speaker can have the initiative in making adjustments. For example,the speaker can choose execution or suspension of the echo cancelingprocessing by the echo canceling processing portion and of the soundcharacteristics information detecting processing of the echo path by thesound characteristics detecting portion, and the sound characteristicsdetecting portion starts processing of detecting the soundcharacteristics information by the instruction from the speaker. In thiscase, by adopting the system on the speaker side including a loudspeakerand a plurality of microphones, in which the level of the output of theloudspeaker is measured by detecting a sound source using the inputvoice signals of the plurality of the microphones and the execution ofthe sound characteristics detecting processing of the echo path by thesound characteristics detecting portion is chosen when the output of theloudspeaker is greater than a predetermined value, a filter coefficientof the echo canceling processing portion can be updated so as not tocancel a voice signal of the speaker but to cancel only the near-endecho signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing an echo canceling system of afirst embodiment of the present invention.

FIG. 2 is a diagram of one example of a specific module configuration,mainly showing an echo canceller 100 according to the present invention.

FIG. 3 shows a structural example of a sound characteristics detectingportion 110 for performing a processing of discriminating a sectioncontaining a voice signal a_(i) serving as a reference signal and thatof a response signal c_(i) containing an echo serving as a comparativesignal.

FIG. 4 is a flowchart showing an example of a process flow of detectingthe section of the response signal containing the echo with respect to avoice by using a cross-correlation coefficient calculation in an echocanceling system of the second embodiment of the present invention.

FIG. 5 shows a structural example of a sound characteristics detectingportion 110 a that can adjust a search range of a cross-correlationcoefficient in an echo canceling system of the third embodiment of thepresent invention.

FIG. 6 is a flowchart showing an adjusting process flow in a searchrange adjusting portion 113 in the echo canceling system of the thirdembodiment of the present invention.

FIG. 7 is a diagram showing a structural example of a device when usinga signal for detecting sound characteristics in the fourth embodiment ofthe present invention.

FIG. 8 shows an echo canceling signal in a simplified manner.

FIG. 9 is a diagram of a structural example of an echo canceling systemof the fifth embodiment of the present invention, mainly showing an echocanceller part.

FIG. 10 is a diagram schematically showing an echo canceling system ofthe sixth embodiment of the present invention.

FIG. 11 is a diagram schematically showing an echo canceling system ofthe seventh embodiment of the present invention.

FIG. 12 shows an example of a recording medium on which a program ofprocessing operations for achieving the echo canceling system of thepresent invention is recorded.

FIG. 13 is a diagram schematically showing a conventional full-duplexcommunication system.

FIG. 14 is a diagram schematically showing an echo canceling systemusing a conventional echo canceller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of an echo canceling system of thepresent invention, with reference to the accompanying drawings.

First Embodiment

In an echo canceling system of the first embodiment of the presentinvention, an echo canceller is installed in a system on a speaker side,so that a canceling processing of an echo generated in a communicationsequipment on a conversation partner side is carried out in the system onthe speaker side, eliminating the need for this processing on theconversation partner side. The echo canceling system of the firstembodiment of the present invention includes a sound characteristicsdetecting portion for detecting sound characteristics information of anecho path seen from the speaker side, and an echo canceling processingportion for canceling an echo by generating an echo canceling signalfrom a voice signal on the basis of the detected sound characteristicsinformation and an inputted tuning signal and superimposing the echocanceling signal on a voice signal returned from the system on thepartner side. In addition, the first embodiment has a configuration alsoprovided with an adjusting portion for receiving an adjustment of theecho canceling processing by the speaker.

FIG. 1 is a diagram schematically showing the echo canceling system ofthe first embodiment of the present invention. In FIG. 1, numerals 10and 20 both denote speakers. For convenience, the following descriptionis directed to an example of the case where the speaker 10 speaks andthe voice of this person is transmitted to the speaker 20 side. Numerals11 and 21 denote microphones, numerals 12 and 22 denote loudspeakers,numerals 13 and 23 denote VoIP applications, numerals 14 and 24 denoteterminals, and numeral 30 denotes the internet.

Numeral 100 denotes an echo canceller, which includes a soundcharacteristics detecting portion 110, an adjusting portion 120 and anecho canceling processing portion 130. As shown in FIG. 1, the echocanceller 100 is incorporated in the terminal 14 on the speaker side.Signals inputted to the echo canceller 100 are a voice signal and aresponse signal returned via an echo path, while a signal outputted fromthe echo canceller 100 is an outputted voice signal to the loudspeaker12. A communication interface and other devices are omitted in thisfigure for convenience.

The sound characteristics detecting portion 110 detects the soundcharacteristics information of the echo path seen from the speaker side.The sound characteristics information of the echo path is detected fromthe voice signal and the response signal returned via the echo path. Forexample, as described below, adjustments are made such that a differencebetween a processed signal obtained by arithmetically processing thevoice signal and the response signal becomes zero, thereby obtaining thesound characteristics information of the echo path.

The adjusting portion 120 receives the adjustment of the echo cancelingprocessing by the speaker and generates the tuning signal.

The echo canceling processing portion 130 generates an echo cancelingsignal from the voice signal based on the sound characteristicsinformation detected by the sound characteristics detecting portion 110and superimposes the echo canceling signal on the voice signal returnedfrom the system on the conversation partner side, thereby canceling theecho. The first embodiment has a configuration in which the echocanceling processing portion 130 generates the echo canceling signalusing the tuning signal inputted via the adjusting portion 120 inaddition to the sound characteristics information detected by the soundcharacteristics detecting portion 110.

FIG. 2 is a diagram of an example of a specific module configuration,mainly showing the echo canceller 100 according to the presentinvention. Numeral 201 denotes a sound characteristics filter includinga FIR filter (finite impulse response filter) etc., numeral 202 denotesa coefficient updating unit, and numerals 203 and 204 denotesubtracters. Numeral 205 denotes a gain controller.

The relationship between each portion in the echo canceller 100 shown inFIG. 1 and the specific module shown in FIG. 2 will be described in thefollowing.

The sound characteristics detecting portion 110 in FIG. 1 corresponds tothe sound characteristics filter 201, the coefficient updating unit 202and the subtracter 203 in FIG. 2. In the present embodiment, the voicesignal is used as a reference signal. The sound characteristicsdetecting portion 110 detects the sound characteristics information ofthe echo path seen from the speaker side from the voice signal (“a” inFIG. 2) serving as the reference signal and the response signal (“c” inFIG. 2) returned via the echo path. For example, as described below, adifferential signal (“e” in FIG. 2) between the signal (“b” in FIG. 2)obtained by arithmetically processing the voice signal by the soundcharacteristics filter 201 and the response signal (“c” in FIG. 2) iscalculated by the subtracter 203. Then, adjustments are made by thecoefficient updating unit 202 such that this differential signal becomeszero. As a result, the coefficient of the sound characteristics filter201 becomes a coefficient for calculation corresponding to the soundcharacteristics information of the echo path.

The adjusting portion 120 in FIG. 1 corresponds to the gain controller205 in FIG. 2, which has an external input system that allows anadjustment by the speaker, so that the speaker can adjust an adjustingamount of the gain controller 205 by him/herself. The gain coefficient“g” can be adjusted in the range, for example, from 0.0 to 1.0. When thegain coefficient “g” is 0.0, the echo canceling processing is notperformed. In other words, the speaker can choose execution orsuspension of the echo canceling processing by the echo cancelingprocessing portion.

The echo canceling processing portion 130 in FIG. 1 corresponds to thesound characteristics filter 201, the gain controller 205 and thesubtracter 204 in FIG. 2. In generating the echo canceling signal, thesound characteristics filter 201, in which the coefficient is adjustedas the sound characteristics detecting portion 110, processes thereceived voice signal (“a” in FIG. 2) arithmetically by reflecting thesound characteristics (“b” in FIG. 2). Then, an adjustment is made bythe speaker with the gain controller 205 so as to generate the echocanceling signal (“g·b” in FIG. 2). Subsequently, in the subtracter 204,the echo canceling signal (“g·b” in FIG. 2) is superimposed on the voicesignal (“c” in FIG. 2) that is returned from the system on the partnerside, in other words, the echo canceling signal is subtracted, therebygenerating a signal (“f” in FIG. 2) in which an echo is canceled, so asto be outputted to the loudspeaker 12.

Now, how the sound characteristics filter 201 updates the coefficientfor simulating the sound characteristics of the echo path will bedescribed in detail. One example is a method of updating the coefficientbased on a learning identification method by using a FIR filter (finiteimpulse response filter) as the sound characteristics filter 201, whichwill be described in the following.

An arithmetic processing by the FIR filter can be expressed by Equation1.

$\begin{matrix}{b_{i} = {\sum\limits_{j = 0}^{n - 1}\;{h_{j}a_{i - j}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

“a_(i)” represents a signal from the microphone 11, namely, an inputsignal to the filter. “b_(i)” represents an output signal of the filter.The subscript “i” represents a sampling number. “h_(j)” represents afilter coefficient, and “n” represents an order.

Next, the update of the filter coefficient h_(j) is expressed byEquation 2.

$\begin{matrix}{{h_{j} = {h_{j} + {\alpha\; e_{i}\frac{a_{i - j}}{{a}^{2}}\mspace{14mu}{where}}}}{e_{i} = {c_{i} - b_{i}}}{{a}^{2} = {\sum\limits_{j = 0}^{n - 1}\; a_{i - j}^{2}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

“α” generally is a constant, and 0.0<α<1.0. “c_(i)” represents aresponse signal from the system on the conversation partner side.

A signal “f_(i)” to be transmitted to the loudspeaker 12 is expressed byEquation 3.f _(i) =C _(i) −g·b _(i)  Equation 3

By using the echo canceling system of the present invention with theabove configuration, it becomes possible to cancel the echo that isheard by the speaker by the echo canceller installed in the system onthe speaker side. The speaker can make fine adjustments to the echocanceling processing for him/herself and enjoy the effect of the echocanceller directly. The optimal echo canceling processing can beexecuted even in the condition with large fluctuation amplitude of thesound characteristics in exchanging the voice signals via the internet.

In addition, the canceling processing of the echo generated in thecommunications equipment on the conversation partner side can be carriedout in the system on the speaker side, eliminating the need for the echocanceling processing on the conversation partner side as conventionallydid. Therefore, it is possible to execute the echo canceling processingin a reliable manner regardless of the condition of a voice processingsystem of the partner.

Second Embodiment

The second embodiment is directed to an echo canceling system in which acontrivance in the sound characteristics detecting processing isincorporated. In this system, a section containing a significant voicesignal serving as a reference signal is detected from a signal receivedfrom the microphone 11 and a section of a response signal containing anecho with respect to a voice is detected from a response signal that isobtained from the partner side and serves as a comparative signal in anaccurate and flexible manner. The first embodiment was described on theassumption that the section containing the voice signal a_(i), servingas the reference signal and the section of the response signal c_(i)containing the echo serving as the comparative signal are fixed.However, the sound characteristics such as a network delay amount arenot fixed in an actual conversation. Therefore, it is necessary todiscriminate where the section containing these signals is. In thesecond embodiment, the section of the response signal containing theecho will be discriminated.

FIG. 3 shows a structural example of the sound characteristics detectingportion 110 for performing a processing of discriminating the sectioncontaining the voice signal a_(i) serving as the reference signal andthe section of the response signal c_(i) containing the echo serving asthe comparative signal. In FIG. 3, the sound characteristics detectingportion 110 includes a power calculation portion 111 and across-correlation coefficient calculation portion 112.

The power calculation portion 111 is used for examining a power in thevoice signal and detecting a part containing a significant voice signalin this voice signal. The power in the received voice signal iscalculated, so that the part having the power greater than apredetermined threshold is regarded as the significant voice signal tobe the reference signal, moving on to the subsequent calculationprocessing of the cross-correlation coefficient with respect to theresponse signal. A wait processing is performed until the signal havingthe power satisfying the predetermined threshold is obtained.

The power calculation by the power calculation portion 111 is expressedby Equation 4.

$\begin{matrix}{{pow}_{i} = {\sum\limits_{j = 0}^{n^{\prime} - 1}\; a_{i - j}^{2}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

“n ” represents an order for the power calculation.

First, the section in the signal to be the reference signal a_(i) isdetermined by Equation 4.

The cross-correlation coefficient calculation portion 112 calculates thecross-correlation coefficient of the voice signal as the referencesignal and the response signal as the comparative signal. Thiscross-correlation coefficient is calculated as Equation 5. A searchrange of the response signal is divided into signal sections“c_((i+k−j))”, so as to search a section in which the cross-correlationcoefficient with the voice signal as the reference signal is largest.The subscript “k” represents an order of the cross-correlationcoefficient, which is, namely, a section number in the range in whichthe cross-correlation is searched. Accordingly, the expansion of therange of “k” widens the range in which the cross-correlation issearched.

$\begin{matrix}{{r(k)} = {\sum\limits_{j = 0}^{n^{''} - 1}\;{a_{i - j}c_{i + k - j}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$where k_(Min)≦k≦k_(MAX). “k_(MIN)” and “k_(MAX)” indicate a presetsearch range, namely, the minimum value and the maximum value of signaldelay of the echo path.

“n” represents an order for the cross-correlation coefficientcalculation.

By calculating “k” where the cross-correlation coefficient r(k)calculated by the cross-correlation coefficient calculation portion 112is largest, it is possible to detect the delay amount of the echo path.

FIG. 4 is a flowchart showing an example of a process flow of detectingthe section of the response signal containing the echo with respect tothe voice by using the cross-correlation coefficient calculationdescribed above.

First, the voice signal a_(i) inputted from the microphone 11 isreceived so as to calculate the power (operation Op401). Whether thepower exceeds the threshold (P_(TH)) is checked. If it does not exceedthe threshold (operation Op402: N), it is judged that the voice signalserving as the reference signal is not inputted, so that the waitprocessing is performed after returning to the operation Op401. If itexceeds the threshold (operation Op402: Y), it is judged that the voicesignal a_(i) serving as the reference signal is inputted, thus moving onto the next operation Op403.

In the operation Op403, the cross-correlation coefficient r(k)betweenthe voice signal “a_(i−j)” serving as the reference signal and thesignal sections c_(si+k−j) of the response signal serving as thecomparative signal is calculated.

In the operation Op404, “k” where the cross-correlation coefficient r(k)of the signal sections calculated in the operation Op403 achieves themaximum value is specified, and the time corresponding to the “k” isregarded as the delay amount of the echo path so as to be the soundcharacteristics information.

In the above configuration, it may be possible that the speaker inputsan instruction whereby the sound characteristics detecting portionstarts processing of detecting the sound characteristics information ofthe echo path.

As described above, in the echo canceling system of the secondembodiment, by searching the signal section where the cross-correlationcoefficient with the voice signal as the reference signal is largest inthe search range of the response signal, it is possible to detect thesection containing the voice signal serving as the reference signal fromthe signal received from the microphone and the section of the responsesignal containing the echo with respect to the voice from the responsesignal that is obtained from the partner side and serves as thecomparative signal in an accurate and flexible manner.

Third Embodiment

The third embodiment is directed to an echo canceling system in which acontrivance in the sound characteristics detecting processing isincorporated. In this system, in detecting sound characteristicsinformation of the echo path by the sound characteristics detectingportion, a threshold and a search range can be adjusted with respect toa correlation value between a reference signal on the speaker systemside and a response signal returned from the conversation partner side.

FIG. 5 shows a structural example of a sound characteristics detectingportion 110 a that can adjust the search range of the cross-correlationcoefficient. In FIG. 5, the sound characteristics detecting portion 110a includes not only the power calculation portion 111 and thecross-correlation coefficient calculation portion 112, but also a searchrange adjusting portion 113.

The search range adjusting portion 113 adjusts the search range of thecross-correlation coefficient. Referring to the second embodiment, itadjusts the range of the order “k” of the cross-correlation coefficient,namely, changes k_(MIN) and k_(MAX) in Equation 5 for calculating thecross-correlation coefficient. As one example, the following adjustingmethod is described. First, a threshold r_(TH) is set for thecross-correlation coefficient r(k). When no coefficient exceeding thisthreshold r_(TH) is obtained as the cross-correlation coefficient withthe voice signal as the reference signal in the search range of theresponse signal, it is regarded that the echo is outside the searchrange of the response signal, in such case as the delay is unexpectedlylarge because of the sound characteristics of the echo path. Thus, thesearch range is adjusted so as to have a wider range.

The following is an example of an adjusting processing in the searchrange adjusting portion 113. FIG. 6 is a flowchart showing an adjustingprocess flow in the search range adjusting portion 113.

First, initial values of k_(MIN) and k_(MAX) representing lower andupper limits of the search range are set (operation Op601).

Steps S602 to S604 are similar to the operations Op401 to Op403 in theflowchart of FIG. 4 in the second embodiment. In order to detect asignificant voice signal section, the power of the signal is calculatedby the power calculation portion 111 (operation Op602), so that thesignal having the power exceeding the threshold is regarded as thereference signal a_(i) (operation Op603). Then, the cross-correlationcoefficient r(k) between the voice signal a_(i−j) serving as thereference signal and the signal sections c_((i+k −j)) of the responsesignal serving as the comparative signal is calculated (operationOp604).

In the third embodiment, “r_(MAX)” where the cross-correlationcoefficient r(k) of the signal sections calculated in the operationOp604 achieves the maximum value is detected (operation Op605). Whetherr_(MAX) exceeds the threshold r_(TH) of the cross-correlationcoefficient is checked (operation Op606). If it exceeds the thresholdr_(TH) (operation Op606: Y), it is judged that a part seemed to be anecho is present in the search range, so that the value of this “k” isregarded as the delay amount based on the sound characteristics of theecho path (operation Op607).

If r_(MAX) does not exceed the threshold r_(TH) (operation Op606: N), itis judged that the part seemed to be an echo is not present in thesearch range of the response signal section of the initial setting. Inorder to expand the search range, the values of k_(MIN) and k_(MAX) areadjusted by setting k_(MIN)=k_(MIN)−α and k_(MAX)=k_(MAX)+β, (operationOp608). Since it is impossible that the value of k_(MIN) is below zero(i.e., an echo is generated earlier), if k_(MIN) is negative (operationOp609: Y), k_(MIN) is regarded as zero (operation Op610). In thismanner, the search range is adjusted so as to return to the operationOp604, where the cross-correlation coefficient is calculated again(operation Op604).

Also, it may be possible that the threshold r_(TH) of thecross-correlation coefficient r(k) and the search range are adjustedwith the help of an operation by the speaker.

As described above, when the sound characteristics detecting portiondetects the sound characteristics information of the echo path, the echocanceling system of the third embodiment can adjust the search rangebased on a calculation result of the cross-correlation coefficientbetween the reference signal in the system on the speaker side and theresponse signal returned from the conversation partner side.

Fourth Embodiment

The fourth embodiment is directed to an echo canceling system in which acontrivance in the sound characteristics detecting processing isincorporated. In this system, the sound characteristics information isdetected using a signal for detecting the sound characteristics. A soundcharacteristics detecting portion includes a signal generating portionfor generating a sound characteristics detecting signal, which serves asa reference signal. Before starting a conversation, the soundcharacteristics detecting portion detects the sound characteristicsinformation of the echo path seen from the speaker side using thereference signal and the response signal returned from the conversationpartner side.

FIG. 7 shows a structural example of a device when using the signal fordetecting the sound characteristics. In the structural example of FIG.7, a sound characteristics detecting portion 110 b includes a soundcharacteristics detecting signal generating portion 114 and a switch115.

It is preferable that the sound characteristics detecting signalgenerating portion 114 generates a signal with a small amount of theauto-correlation such as pulse or white noise as the reference signal.Also, in order to generate a user-friendly tone, music that does notannoy the user may be used. It is also preferable that the tone having afrequency higher or lower than an audio frequency band is used so as notto be heard by a user.

The switch 115 switches whether or not the sound characteristicsdetecting signal generating portion 114 is used in the soundcharacteristics detecting portion 110 b. For example, in a phase ofdetecting the sound characteristics information at the beginning of theconversation, the side of the sound characteristics detecting signalgenerating portion 114 is turned on so as to adjust the value of thesound characteristics filter according to the sound characteristics,while in a phase of an echo canceling processing, the side of themicrophone 11 is turned on.

With the above configuration, it is possible to use a signal suitablefor detecting the sound characteristics information, thereby detectingthe sound characteristics information of the echo path in an accuratemanner.

However, when using the sound characteristics detecting signal, it isnecessary to perform processings such as the transmission of the soundcharacteristics detecting signal and receipt of the echo sound, and thedetermination of the coefficient of the sound characteristics filterbefore starting the actual conversation. Accordingly, it also may bepossible that, instead of a particular sound characteristics detectingsignal, a voice signal inputted in the conversation is used as thereference signal, so that the sound characteristics detecting portiondetects the sound characteristics of the echo path seen from the speakerside using this reference signal and the response signal returned fromthe conversation partner side. This makes it possible to detect thesound characteristics information constantly or at a fixed time intervalduring the conversation, thereby updating the sound characteristics ofthe echo path. Consequently, the optimal echo canceling processingalways can be executed even when the sound characteristics vary.

Fifth Embodiment

The fifth embodiment is directed to an echo canceling system in which acontrivance in the echo canceling signal generating processing isincorporated. In this system, the echo canceling signal used in the echocanceling processing of the echo canceling processing portion is dividedinto a delayed part and a signal part following the delayed part, sothat the former is processed by a delay filter and the latter isadjusted by a FIR filter or the like. As described above, the echocanceling signal is divided into the delayed part and the signal partfollowing the delayed part so as to be processed arithmetically, therebyreducing a processing amount.

FIG. 8 shows the echo canceling signal in a simplified manner. t=0indicates a timing when a sound characteristics detecting signal, forexample, a pulse is inputted in a microphone in a speaker's system. Asshown in FIG. 8, the echo canceling signal can be divided into a delayedpart 801 and a signal part 802 following the delayed part 801. In thisexample, a delay sample number is “d”. In the example of the firstembodiment, an echo canceling signal having a form shown in FIG. 8 isgenerated by the learning identification method by using the soundcharacteristics filter 201 and the coefficient updating unit 202 shownin FIG. 2. On the other hand, in the fifth embodiment, the delayprocessing corresponding to the delayed part 801 is executed by thedelay filter and the signal part corresponding to the signal part 802 isgenerated by the sound characteristics filter 201 such as the FIRfilter. The signal is divided into the delayed part 801 and the signalpart 802 following the delayed part 801 so as to be processedarithmetically, thereby achieving the processing amount smaller thanthat needed when processing a signal as an integral signal as in thefirst embodiment.

FIG. 9 is a diagram of a structural example of the echo canceling systemof the fifth embodiment, mainly showing an echo canceller part. In FIG.9, numeral 210 denotes a delay detector, and numeral 220 denotes a delayfilter. The other elements are similar to those in FIG. 2 in the firstembodiment, so the description thereof is omitted in this embodiment.

The delay detector 210 calculates the delay amount in the echo path. Forexample, a pulse signal is inputted from a microphone 11 at t=0 in asilent state, and the presence of a significant voice signal is detectedin a response signal by the power calculation portion described in thesecond embodiment or the like. Then, the delay detector 210 maycalculate the delay amount of this response signal. It is assumed thatthe delay amount “d” is detected in this embodiment.

The delay filter 220 provides a delay corresponding to the delayed partin the echo canceling signal. Based on the delay amount “d” that iscalculated by the delay detector 210, the delay filter 220 is set sothat the transfer function thereof in the Z region is Z^(−d).

After the voice signal is subjected to the delay processing by the delayfilter 220, processings are similar to those in the first embodiment. Inadjusting the coefficient of the FIR filter, a signal “m” that has beensubjected to the delay processing is processed arithmetically by thesound characteristics filter 201, then subjected to a subtractingprocessing with respect to the response signal by a subtracter 203. Thecoefficient of the FIR filter is adjusted via the coefficient updatingunit 202 such that the difference is zero. In the echo cancelingprocessing, by using the sound characteristics filter 201 whosecoefficient has been adjusted, the signal that has been subjected to thedelay processing is processed arithmetically, then subjected to a gainadjustment by a gain controller 205, so that the signal that has beensubjected to the echo canceling processing is outputted to theloudspeaker 12. The echo canceling processing and the adjustingprocessing of the FIR filter coefficient described above achieve theprocessing amount smaller than that needed when arithmeticallyprocessing the voice signal as an integral signal as described in thefirst embodiment.

The elements described in the above embodiment also can be supplied as ahardware module. It also is possible that a processing program thatachieves the processings of the above elements is described so that ageneral purpose microprocessor or the like can achieve such processings.

Sixth Embodiment

Although a plurality of microphones are used in the followingdescription, either a microphone array or a plurality of microphones maybe used.

In the echo canceling system according to the sixth embodiment, a systemon a speaker side includes a loudspeaker and a plurality of microphonesand performs a synchronous addition of input voice signals of theplurality of the microphones with respect to the direction of thespeaker so as to enhance a voice signal intentionally, thereby improvingan accuracy of the echo canceling system. A microphone sensitivity to avoice of the speaker is made higher than that to an output of theloudspeaker in the system on the speaker side, so as to weaken anacoustic coupling between the loudspeaker and the microphones, therebyreducing an influence of, what we call, a near-end undesirable path ofthe voice.

FIG. 10 shows a schematic configuration of the echo canceling system ofthe sixth embodiment. The configuration indicated by numerals 20 to 24constituting the system on a conversation partner side, which was shownin FIG. 1, is omitted in this figure.

Although two microphones 11 a and 11 b are provided in the configurationof FIG. 10, three or more microphones may be provided. The microphones11 a and 11 b are provided with delay units 15 a and 15 brespectively.Numeral 16 denotes an adder.

The delay amounts of the delay units 15 a and 15 b are set such thatdirectionality of the respective microphones 11 a and 11 b matches anassumed direction of a speaker 10. Outputs of the delay units 15 a and15 bare both inputted to the adder 16. A synchronous addition in theadder 16 enhances a voice signal from the speaker and cancels out voicesignals from the other directions (noise). In this example, it cancelsout an echo signal outputted from the loudspeaker 12 that is returnedbecause of a far-end undesirable path. The output signal that issubjected to the synchronous addition as described above is transmittedto an echo canceller 100 and a VoIP application 13. The echo canceller100 and the VoIP application 13 may be the ones described in the firstto fifth embodiments.

Seventh Embodiment

Although a plurality of microphones are used in the followingdescription, either a microphone array or a plurality of microphones maybe used.

In the echo canceling system according to the seventh embodiment, asystem on a speaker side includes a loudspeaker and a plurality ofmicrophones and performs a synchronous subtraction of input voicesignals of the plurality of the microphones with respect to thedirection of the loudspeaker so as to cancel out a near-end echo signaloutputted from the loudspeaker, thereby improving an accuracy of theecho canceling system. A microphone sensitivity to an output of theloudspeaker in the system on the speaker side is made lower, so as toweaken an acoustic coupling between the loudspeaker and the microphones,thereby reducing an influence of, what we call, a near-end undesirablepath of the voice.

FIG. 11 shows a schematic configuration of the echo canceling system ofthe seventh embodiment. The configuration indicated by numerals 20 to 24constituting the system on a conversation partner side, which was shownin FIG. 1, is omitted in this figure.

Although two microphones 11 a and 11 b are provided in the configurationof FIG. 11, three or more microphones may be provided. The microphones11 a and 11 b are provided with delay units 15 a and 15 brespectively.Numeral 17 denotes a subtracter, and numeral 18 denotes a delay amountcontroller.

The delay amounts of the delay units 15 a and 15 b are set to match thedelay amounts of voice signals that reach the respective microphones 11a and 11 b from the direction of the loudspeaker 12. The delay amountcontroller 18 adjusts those delay amounts. Outputs of the delay units 15a and 15 b are both inputted to the subtracter 17. A synchronoussubtraction in the subtracter 17 cancels out the voice signals from thedirection of the loudspeaker 12. In other words, it eliminates an echosignal that is returned because of a far-end undesirable path andoutputted from the loudspeaker 12. The output signal that is subjectedto the synchronous subtraction as described above is transmitted to anecho canceller 100 and a VoIP application 13. The echo canceller 100 andthe VoIP application 13 may be the ones described in the first to fifthembodiments.

Eighth Embodiment

The echo canceling system according to the present invention can beconfigured using various computers by providing a program including theprocessing operations for realizing the configurations as describedabove. When loading the program provided with the processing operationsrealizing the echo canceling system according to the present inventioninto the computer, the recording medium on which such program isrecorded may be read by the computer or can be downloaded from anetwork. For example, as shown in FIG. 12, a portable recording medium301 such as a CD-ROM 302 or a flexible disk 303 can be read by acomputer 304 or downloaded from a recording medium 300 in a recordingapparatus on the network. Also, it may be stored in a recording medium305 such as a hard disk or a RAM in the computer 304 from the beginning.When executing the program, this program is loaded into the computer 304and executed in its main memory.

In the first to eighth embodiments, it is possible that the soundcharacteristic detecting portion starts processing of detecting thesound characteristics information of the echo path by the instructionfrom the speaker. It is also possible that a threshold and a correlationsearch range with respect to a correlation value between the referencesignal on the speaker system side and the response signal returned fromthe conversation partner side can be adjusted by an operation of thespeaker.

With the above configuration, the speaker can have the initiative inacknowledging the start of the echo canceling processing and inadjusting the echo canceling processing.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1. An echo canceling system for a full-duplex communication systemcomprising: a sound characteristics detecting portion detecting soundcharacteristics information of an echo path seen from a speaker side; anecho canceling processing portion canceling an echo included in a signalreturned from a system on a conversation partner side based on the soundcharacteristics information detected by the sound characteristicsdetecting portion; the sound characteristics detecting portion and theecho canceling portion being installed in a communication system not onthe conversation partner side but on the speaker side; and an adjustingportion receiving a tuning signal of an echo canceling processing from aspeaker, wherein the echo canceling processing portion cancels the echousing the tuning signal in additional to the sound characteristicsinformation detected by the sound characteristics detecting portion. 2.The echo canceling system according to claim 1, wherein the soundcharacteristics detecting portion comprises a signal generating portionfor generating a sound characteristics detecting signal, which serves asa reference signal, and before starting a conversation, the soundcharacteristics detecting portion detects the sound characteristicsinformation of the echo path seen from the speaker side using the soundcharacteristics detecting signal and a response signal returned from theconversation partner side.
 3. The echo canceling system according toclaim 3, wherein, in detecting the sound characteristics information ofthe echo path by the sound characteristics detecting portion, athreshold and a correlation search range with respect to a correlationvalue between the reference signal in the system on the speaker side andthe response signal returned from the conversation partner side can beadjusted.
 4. The echo canceling system according to claim 1, wherein avoice signal inputted during a conversation is regarded as a referencesignal, and the sound characteristics detecting portion detects thesound characteristics information of the echo path seen from the speakerside using the voice signal and a response signal returned from theconversation partner side.
 5. The echo canceling system according toclaim 4, wherein, in detecting the sound characteristics information ofthe echo path by the sound characteristics detecting portion, athreshold and a correlation search range with respect to a correlationvalue between the reference signal in the system on the speaker side andthe response signal returned from the conversation partner side areadjusted.
 6. The echo canceling system according to claim 1, wherein anecho canceling signal used in the echo canceling processing of the echocanceling processing portion is divided into a delayed part and a signalpart following the delayed part, and the echo canceling processingportion includes a delay filter for providing a delay corresponding tothe delayed part and a signal filter for generating a signalcorresponding to the signal part.
 7. The echo canceling system accordingto claim 1, wherein the system on the speaker side comprises aloudspeaker and a plurality of microphones and performs a synchronousaddition of input voice signals of the plurality of the microphones withrespect to a direction of the speaker so as to enhance a voice signal.8. The echo canceling system according to claim 1, wherein the system onthe speaker side comprises a loudspeaker and a microphone array or aplurality of microphones and performs a synchronous subtraction of inputvoice signals of the microphone array or the plurality of themicrophones with respect to a direction of the loudspeaker so as tocancel out an echo signal outputted from the loudspeaker.
 9. The echocanceling system according to claim 1, wherein the speaker can chooseexecution or suspension of the echo canceling processing by the echocanceling processing portion and of the sound characteristics detectingprocessing of the echo path by the sound characteristics detectingportion.
 10. An echo canceling processing program performing echocanceling processing for a full-duplex communication system, the programcomprising program codes of: a sound characteristics detectingprocessing operation detecting sound characteristics information of anecho path seen from a speaker side; an echo canceling processingoperation canceling an echo included in a signal returned from a systemon a conversation partner side based on the sound characteristicsinformation detected in the sound characteristics detecting processingoperation; the sound characteristics detecting portion and the echocanceling portion being installed in a communication system not on theconversation partner side but on the speaker side; and an adjustingoperation receiving a tuning signal of an echo canceling processing froma speaker, wherein the echo canceling processing portion cancels theecho using the tuning signal in addition to the sound characteristicsinformation detected by the sound characteristics detecting portion. 11.An echo canceling processing program readable by a computer forcontrolling the computer to perform echo canceling processing for afull-duplex communication system, by: detecting sound characteristicsinformation of an echo path seen from a speaker side; canceling an echoincluded in a signal returned from a system on a conversation partnerside based on the sound characteristics information detected in thesound characteristics detecting processing operation; the soundcharacteristics detecting and the echo canceling being performed in acommunication system not on the conversation partner side but on thespeaker side; and receiving a tuning signal of an echo cancelingprocessing from a speaker, and controlling the echo canceling processingto cancel the echo using the tuning signal in addition to the soundcharacteristics information detected by the sound characteristicsdetecting.